This week in science is a review of the most interesting scientific news of the past week.

Cross section of the Great Pyramid showing the location of the void. Source: ScanPyramids Mission.

Muons were used to detect possible hidden chamber inside the Great Pyramid

Muons are elementary particles like electrons, with the same electric charge and spin, but with a greater mass and unstable. They originate from the interactions of cosmic rays with the atoms in the upper atmosphere and come down to the ground at almost the speed of light. Even though they can penetrate dense materials, like rocks, they are harmless to humans and other living beings.

Muography is a technique suggested by archaeologist Luis Alvarez back in the 1960s, in which muons would be used to study the interior of pyramids. Unfortunately, the technology required to perform the technique was not available back then, but nowadays it is widely used by archaeologists, geologists, and the military. For example, it was used to assess damage at the Fukushima nuclear power plant after the disaster in 2011.

A 3D reconstruction of the void and augmented reality were used by the researchers. Source: ScanPyramid Mission.

By using muography, scientists from the ScanPyramids project have confirmed last week the presence of a large empty space within Khufu’s pyramid, the largest pyramid in Giza. The large and inaccessible void within the structure measures at least 30 meters (100 feet) in length, right above the already known Great Gallery, and could signal the presence of a possible hidden chamber although that remains speculative for now.

Scientists now plan on doing more muography scans of the pyramid to find out more about the hidden structure and possible hidden adjoining corridors. Also, the ScanPyramids team is currently designing a robot capable of squirming through a very small hole and flying once inside the cavity.

The United Nations' World Meteorological Organization (WMO) released last week its annual Greenhouse Gas Bulletin, indicating that the concentration of carbon dioxide in the atmosphere has hit a new high last year, reaching 403.3 parts per million. The concentration is up from 400ppm in 2015, due to both the strong El Niño event and human activities.

According to the bulletin, “the rate of increase of atmospheric CO2 over the past 70 years is nearly 100 times larger than that at the end of the last ice age”. As stated by Petteri Taalas, secretary-general for the World Meteorological Organization:

"Without rapid cuts in CO2 and other greenhouse gas emissions, we will be heading for dangerous temperature increases by the end of this century, well above the target set by the Paris climate change agreement […] The laws of physics mean that we face a much hotter, more extreme climate in the future […] Future generations will inherit a much more inhospitable planet."

Finally, the bulletin also states that the last time Earth’s atmosphere contained a similar concentration of carbon dioxide was three to five million years ago, according to geological records. Back then, the sea level was between 10 and 20 meters higher than nowadays.